The present invention relates to a tubular light transmitting element capable of efficiently transferring optical energy such as solar energy converged by an optical system to any desired location. The present invention also relates to an optical energy collecting and transmitting apparatus using such a tubular element.
Various techniques have heretofore been proposed by the applicant in order to converge light from a light source such as sunlight into a light transmitting element by means of an optical system such as a lens, so that the light may be transmitted through the element to a desired place for the purpose of illumination or the like. In effectively introducing sunlight converged by the optical system and transmitting the light effectively with a minimum of loss throughout the transmission path, it is a prerequisite that the light transmitting element be made of a material which causes least attenuation to light and, therefore, features excellent transmissibility. Such materials may be typified by silica glass or fused silica, as well known to the art. Silica glass, however, is quite expensive and so will be a light transmitting element used in, for example, a sunlight supply device which the applicant has proposed and require a large number of such elements. Thus, the use of silica glass for light transmitting elements have so far failed to be readily practiced. Where sunlight is converged by a lens or like optical system, it is impossible to focus all the wavelength components thereof to one point due to the chromatic aberration with the result that the focussed image of the sun inevitably has certain largeness. Stated another way, it is quite difficult to introduce into an optical fiber all the solar energy converged by the optical system. Though a substantial amount of optical energy may be transferred efficiently if use is made of a light transmitting element having a larger diameter, the consumption of a large amount of expensive silica glass would render the cost prohibitive and make it difficult to achieve the efficient transmission of optical energy. Besides, the resulting optical fiber would be very heavy to make the transportation or installation thereof troublesome.